Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $187.38   10.106%   $206.3166   $206.32   $206.30   $206.30  
  Purchase #2 $5.49   8.530%   $5.9583   $5.96   $5.95   $6.00  
  Purchase #3 $124.35   8.737%   $135.2145   $135.21   $135.20   $135.20  
  Purchase #4 $154.91   10.790%   $171.6248   $171.62   $171.60   $171.60  
  Purchase #5 $237.79   5.216%   $250.1931   $250.19   $250.20   $250.20  
  Purchase #6 $245.29   13.331%   $277.9896   $277.99   $278.00   $278.00  
  Purchase #7 $27.48   5.677%   $29.04   $29.04   $29.05   $29.00  
  7 purchase totals = $982.69       $1,076.3369   $1,076.33   $1,076.30   $1,076.30